# std::experimental::make_unique_resource_checked

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< cpp‎ | experimental‎ | unique resource

Defined in header `<experimental/scope>` |  |
template< class R, class D, class S = std::decay_t<R> > std::experimental::unique_resource<std::decay_t<R>, std::decay_t<D>> make_unique_resource_checked( R&& r, const S& invalid, D&& d ) noexcept(/*see below*/); |  | (library fundamentals TS v3)

Creates a `unique_resource`, initializes its stored resource handle is initialized with std::forward<R>(r) and its deleter with std::forward<D>(d). The created `unique_resource` owns the resource if and only if bool(r == invalid) is false.

The program is ill-formed if the expression r == invalid cannot be contextually converted to bool, and the behavior is undefined if the conversion results in undefined behavior or throws an exception.

### Paramaters

r | - | a resource handle
d | - | a deleter to use to dispose the resource
invalid | - | a value indicating the resource handle is invalid

### Reture value

A `unique_resource` described above.

### Exceptions

Any exception thrown in initialization of the stored resource handle and the deleter.

`noexcept` specification:
noexcept(

std::is_nothrow_constructible_v<std::decay_t<R>, R> &&
std::is_nothrow_constructible_v<std::decay_t<D>, D>

)

### Notes

`make_unique_resource_checked` exists to avoid calling a deleter function with an invalid argument.

Resource handle r is either copied or moved into the return value, and the created `unique_resource` always holds an underlying resource handle with object type.

### Example

Run this code

    #include <cstdio>
    #include <experimental/scope>

    int main()
    {
        // avoid calling fclose when fopen fails
        auto file = std::experimental::make_unique_resource_checked(
            std::fopen("potentially_nonexistent_file.txt", "r"),
            nullptr,
            [](std::FILE *fptr) { std::fclose(fptr); }
        );
        if (file.get())
            std::puts("The file exists.");
        else
            std::puts("The file does not exist.");
    }

Possible output:

    The file does not exist.

### See also

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